Signal receiving apparatus



Nov. 8, 1938.

G. l., BEERs `SIGNAL RECEIVING APPARATUS Filed Jan. 31, 1931 lllll VIII' www INVENTOR George Leers,

' '/s ATTORNEX Patented Nov. 8, 1938 PATENT OF F ICE SIGNALv RECEIVINGr APPARATUS `George Lisle Beers, Collingswood, '-N.- J., assignoig by mesne assignments, -to Radio Corporation of America, New York, Nj Y., a corporation of Delaware 'Application"JanuaryV 31, 1931, SerialV No.1 512,653

`3.2 Claims. (Cl. Z50-120) IE--My inventionfrelatesto- 'signal receiving apy Lparatus and it has particular relation to devices `-for' preventing theresponse of suchapparatus feto-signals-ofamplitude less than a-predetermined "Itfhas, previously,l been proposed to provide jsign'al-receivingI apparatus with automatic' volume-control devices whereby the ultimate sound ioutputisnrendered substantially independent of A""" fadingfand other phenomenar Which tend to cause llthe L amplitude yof`- an incomingl signal tor greatly "vary 'In the operation of`=receiversequipped with'automaticl volume-control devices, however, some dissatisfaction `has been experienced by L15 reason of the fact that, during the operation of 'f manually or automatically'tuning the system from one' desiredfstation` to-another, intervening "-fstationsarereceived. lFurthermore, during the tuningoperation,y there is always present, from a Wide variety off-sources,- objectionable inter- `hlference-of the type i' generally vdesignated as -background noise. t

Itis, accordingly-*an objectof` myinvention toprovidemeans whereby a portion of la-radio .25 receiver isf-rendered inoperative during the tun fing operation.

`Pr`Another object; of rmy '-inventionis yto provide "'means'whereby backgroundA noise shall'be elimyfinated vduring the operation "of tuning a signal 3.230- receiving systemv fromone desired station toanothenstation "Another -ob-,iect ofmyinvention kis to provide, v--in a-vsignal'receiving system of the type includingA automatic' volume-control devices, `means re- ;E35ffsponsivetosaid `vdevices for eliminating backe ground noise.

-A further object of Amy'invention is to provide, -in1a-"system ofthe type described, means that f-sh'all give a visual indication of the tuning of "flOuthe system to yexactisyntony vwith signals from'a 'desired station.

A still further and more specic object of my Iinvention is to provide, lin a systemof'the type -1 described, --wherein a tuning indication device is '.ll'iincludedgmeans for illuminating thefsaid'devicelat such timesas the-system' isf-being'tuned to syntonyf'vvith a desi-redsignal and additional illuminating means -forfin'dicatng thatthe said desired signal is: being: received Aat predetermined The aforementioned objects and-other objects ffappurtenant lthereto, ':I "prefer to l.accomplish through-the. medium of fa grid-controlfrect'ifyi ing device `having;characteristics similar to ythose :55 :of: ,thefdeviceccommercially?designatedas a Thyratron. 'In the Gen'eralfElectric Review for April @1929,@pagel 213, devices #of the character prefferred-'asrectiersare dened as electrostatically."controlled'arc -rectiers and such term will be used hereinafter 'to refer to that type of defvifce or tube. `V The 'rectifyingdevice is supplied with"alternating potential and the grid thereof Visfnorrnally so biased that rectified current flows in lthe output circuit. The grid of the rectifier `devicei's so-1 connected to theplate terminal of a f resistor included inthe output circuit of a volume-'control tube, that the-drop in potential across thesaid resistor, when current flows there- Yin,l shall compensate the normal bias applied to the device with the result that it becomes non- 'f conductive.

`The volume-control tube is supplied with signal energy from amplifiers which precede it, the

vpresence of avsignal of proper amplitude causing 'thefsaid tube-to Abecome more conductive than* normal with the result that current iiows in the output resistor'referred to.

If further interpose alight-source in the output circuit of the rectifier or so arrange the said source that the lapplication of energy thereto is controlled lby current in the said output circuit andfI so dispose the `light-source that it illu- 'minates at least a portionv of the tuning-indicaitsmetl'lod of operation, vtogether Withadditional'objects andl advantages, ywill best be under- "stood from the following description of a specic embodiment and certain variants thereof, when read in connection with the accompanying drawing.

lf'hesingle gure of the drawing is a diagrammaticview of aportion of a radio receiving sys- "tern of V'the i superheterodyne type including an embodimentof my invention.

The apparatus illustrated in the drawing com@ prises a volume-control tube l, a rectifier devicesuch asian electrostatically controlled arc rectier providing a vbackground noise suppressor tube- 3 having vcharacteristics hereinbefore revferredto, anda second 'detector tube 5 which `represents any suitablev electric discharge amplier device located in the signal circuit of the apparatus.

The volume-control tube is provided with' an v'input circuit constituted' by an inductor l and .altuning condenser 9, one end ofthe in-f ductor being connected by a conductor Il to the grid of the second detector tube 5 and the other end of the inductor being connected through a resistor I3 and a light-source I5, such as a small incandescent lamp, to a point Il on a Voltage dividing resistor I9 which is negative with rey Y occasioned by the ow of space current therein,

together With the drop between points I1 and 2l, normally biasing the second detector to substantially the cut-off point.

The second detector is supplied with plate potential from the voltage dividing resistor I9, the

primary winding 21 of an audio frequency transformer 2S being included in the supply circuit.

The light-source I5 referred to is also included in the output circuit of the rectier, the said rectifier being supplied with plate potential from any convenient AC source (not shown).

The output circuit of the volume-control tube includes a resistor 3|, one en-d of which is connected to the plate of the said tube and, through a resistor 32 to the grid of the rectifier, and the other end of which is connected to a point 33 on the voltage dividing resistor I9 which is at a positive potential with respect to a point 35 thereon to which a conductor 31, leading from the cathode of the volume-control tube, is connected.

The resistor32 serves to prevent the rectifier grid-current from affecting the bias applied to the amplifier tubes.

yThe volume-control tube is supplied with variable grid bias potential through a connection, Y

including a resistor 39, which extends between the grid thereof and a movable contact arm 4I associated with a portion of the voltage dividing resistor that is more negative than the point 35 to which the cathode isl connected.

A conductor 43 extends from the plate of the volume-control tube tothe grid circuits of preceding amplifying tubes (not shown) for the 'purpose of supplying an increasing negative bias thereto in response to increasing signal amplitudes and a plurality vof conductors 45, 41 and 59, extend from the voltage dividing resistor to the cathode and plates of the said amplifying tubes respectively.

The light-source is preferably disposed in proximity to the rear face of a translucent tuningin-dication device 5l or dial, a mask 53 being optionally disposed between the source and the said dial to limit the area illuminated. Y

In theoperation of my improved signal receiving system, the plate of the rectifier or noise suppressor tube 3 is supplied with an alternating potential of 300 volts Which potential may, conveniently, be derived from va secondary winding of the power transformer (not shown) which energizes the power rectifier (not shown) Ato supply the voltage dividing resistor and the cathode heating circuits of the system. IThe rectifier 3 is normally so biased by adjustment kof the points 33 and I'i on the voltage dividing resistor to which the grid and cathode are respectively connected that, when no signal is beingY impressed upon the input circuit of the volume-control tube from the preceding amplifying tubes, current flows in the output circuit thereof and causes the light-source to be energized. The fall in potential across the light-source is in such direction as to increase the normal negative potential applied to the grid of the second detector tube to far beyond the cut-oi point, thus preventing it from operating. n

As soon as a signal of predetermined amplitude is received, increased current .ows in the output resistor 3l of the volume-control tube., which functions as an anode-bend detector, causing a drop in potential across the output resistor in' Y such direction as to render the grid of the rectifier more negative. Upon the grid of the thyratron becoming sufficiently negative, the device is `rendered non-conductive and output current therefrom ceases.

The cessation of current-flow through the light-source removes the additional negative potential added thereby to the input circuit of the second detector tube, thus permitting the said tube to become operative to demodulate signals `impressed upon the input circuit thereofV from the preceding amplifying tubes. At the same time,-the tuning dialis deprived of illumination,

thus indicating that a signal of predeterminedr amplitude is being impressed upon the second detector tube from the preceding tubes in the system.

It has been found that in the operation of the system described, the grid controlled rectifier device 3, when provided by a type of electro-V statically controlled arc rectifier known comrnercially as a Thyratron, .and in conjunction n with an input grid circuit lterjincluding a resistor 32, the rectifier deviceroperates withan.

appreciable hysteresis effect so that the voltage required to start the device is substantially great-*- er than the voltage required to maintain it in operation after it has once been started.r VThis is a desirable characteristic since it tends to.

stabilize the operation in response to small variations in signal intensity at a critical operating point.' In conjunction with a rectier device of the above type, the filter means, including Ythe resistor 32, isY effective as a stabilizing means.r n It has also been found that the grid lter means for the signal transmission device, or second detector 5, which grid lter means includes the resistor I 3, prevents Yarapid change in grid. potential and thereby prevents noisy operationv of the circuit which would ordinarily'be occasioned by too. rapid change in the grid potential of the signal transmitting device. With this'resistor interposed between the variable source of Y vent an indication of signals tuned in,.for Vthe reason that the indicating device I5 is responsive instantly to signals. The system just includes a quick acting device and a slow acting de-v tector device.

' It also lies within the scope of my invention to' substitute a resistor for the light-source I5 and to so control the application of energy to the said vce source from anappropriatebattery or the like, 376

by; meansof relays or equivalent devices, that thegdialisilluminated only when the signal is properly tuned in and not during the tuning operation, as just described.

It alsoiisffeasible tok provide a plurality of lightsources, one or more of which are under control of the ,rectiiien whereby the dial is generally illuminated during the tuning operation an-d a circumscribed area thereof, on which call-letters are visible, -is illuminated by light of a different colorfor byy light from an auxiliary, constantly energized source, when the tuning operation is complete- It. will beapparent, from the foregoing, that I have, by my invention, provided a system wherebythe operation of tuning a signal receiving systemisrender-ed entirely free from background noise and from'interferences by signals emanating f romundesired stations, and one whereby a positive indicationr of the presence of a desired signal is given.

n My improved system is alsoadaptable to powercontrol by incoming radio signals. In such event,

the-tuning isiixed and the rectifier output cur-v rent is used for the actuation of the control-circuits.y

Although I have illustrated and described a speciiic embodiment of my invention, many modiiications thereof 4will be apparent to those skilled in the art to which it pertains. invention, therefore, is not to be limited except insofar as is necessitated bythe prior art and by the spirit of the appended claims; l

I. claim as my invention:

1. In signal receiving apparatus including demodulating means, means for supplying signal potentials to said demodulating means including an adjustable tuning reactor, and signal responsive means for applying an additional potential to said demodulating means to render said demodulating means substantially inoperative during adjustment of said reactor and for restoring said demodulating means yto operation in response to signals ofl a predetermined amplitude.

r2. In signal receiving apparatus including a detector, means forsupplying signal potentials to said detector including an adjustable reactor, and signal responsivemeans for applying an additional potential to said detector to render saidA detector substantially inoperative during adjustment of said reactor and for restoring said de'- tector to operation in response to signals of a predetermined amplitude.

3. In combination, an amplifier, a detector, means for supplying signals to said detector and signal responsive means for applying a controlling potential to said detector to render said detector Vinoperative when the the signal delivered thereto by. said amplifier is below a predetermined amplitude and for restoring said detector to operation when the signal delivered thereto is above said amplitude.

4.*In combination, an amplifier, a detector, means for supplying signal potentials to said detector, and vseparate signal responsive means forv applying an additional potential to said detector to render said detector inoperative when a signal delivered thereto by said amplifier is below a pre-determined amplitude, said means being responsive for restoring said detector to operationwhen said signal is above said amplitude, said means including a grid-controlled rectifier device, and a resistor filter means in the grid circuitv of said device.

5. In, combinat,ion,- an, amplifier, a detector,

means' for supplying signal potentials to said detector, separate signal responsive means for applying an additional potential to said detector to render said detector inoperative when a signal delivered thereto by said ampliiier is below a predetermined amplitude, said means being responsive Ior restoring said detector to operation when said signal is above said amplitude, and a tuning indicator including a current responsive light source having a potential drop producing impedance for providing said additional controlling potential.

6. In signal receiving apparatus including demodulating means, means for supplying signal potentials to said demodulating means including an adjustable tuning reactor, signal responsive means for applying an additional potential to said demodulating means to render said demodulating means substantially inoperative during adjustments of said reactor and for restoring said demodulating means to operation in response to signals lof a predetermined amplitude, and elec'- trical means in circuit with said last named means providing a light source for indicating the tuning of the apparatus, the said light source being f connected with and under the control of the said means for contro-lling the demcdulator means.

. 7. In a signal-receiving apparatus, a detector device having a control grid circuit, a light source connected in said circuit, a time delay filter means in said circuit between said light source and said detector, a grid controlled rectifier device connected in circuit with said light source to control the flow of current therethrough, circuit means for supplying alternating current through said rectifier device to said light source, a signal responsive automatic volume control .means having an output circuit, a grid circuit for said rectifier device connected with said output circuit to receive controlling potentials therefrom, and means for supplying signals to said automatic volume control means, said means including a tuning reactor.

8. In a radio signal receiving system having automatic volume control means, the combination of a detector tube, means providing a biasing potential normally rendering said detector inoperative torectify signals, and means including a grid controlled rectifier device controlled by said automatic volume control means for reducing said biasing potential to a value whereat said detector is operative in response to signals of a predetermined amplitude.

9. In signal receiving apparatus, tuning means, a potential source, tuning indication means operatively connected with said tuning means, a light source so disposed as to be capable of illuminating at least a portion of said indicating means, signal controlled means for substantially depriving said light source of potential when said tuning means is adjusted to syntony with a desired signal, and an electric discharge device in the signal channel of said apparatus, said device having a control grid circuit, said light source being included in said grid circuit and providing potential-drop producing impedance means therein, thereby to control said device in transmission of signals.

l0. In a radio signal receiving system having automatic volume control mea-ns, the combination of a detector tube, means providing a biasing potential normally rendering said detector inoperative to rectify signals, means including a grid controlled rectifier device controlled by said automatic volumecontrol means for reducing said biasing potential to a value whereat said detector isoperative in response to signals ofv a pre-determined amplitude, and said last named means further including an indicating lamp in series with said rectifier device having an impedance from which said potential is derived. Y

11. In a signal-receiving apparatus, the combination with a tuning indicator and an electric discharge device in the signal circuit of said apparatus for controlling the transmission of signals therethrough, said device having a control grid circuit, of a lamp connected in said grid circuit and associated with said tuning indicator, said lamp being adapted to provide a potential drop in operation sumcient to bias said device to a point whereat it is inoperative to transmit signals, a time delay lter means interposed between the lamp and said device, an electrostatically controlled arc rectifier device connected in circuit with said lamp for controlling the ow of current therethrough, a control grid circuit for said rectifier device, and signal responsive means connected with said grid circuit for supplying controlling potentials thereto of a magnitude sufficient to bias said device to cut-off in response to signals above a predetermined ammission channel of the apparatus connected with said lamp for receiving a biasing potential therefrom.

13. In a signal-receiving apparatus, means for controlling the transmission of signals to said apparatus and for providing a visual indication of said signals, said means including an electric tuning indicator lamp, a signal controlled rectier device for supplying current thereto, an elec'- tric discharge signal amplifier device in the signal transmission channel oi the apparatus connected with said lamp for receiving-a biasing potential therefrom, a control grid circuit for each of said devices, and a lter means in each of said circuits.

14. In a signal-receiving apparatus, the combination of a signal indicating circuit, a grid controlled rectier device for Vsupplying current thereto, a potential drop producing element in said circuit, an electric discharge signal amplier device connected with said element to receive a controlling potential therefrom, said device being in the signal channel of the receiving appaf ratus thereby to control the flow of signals therethrough, and signal responsive means for controlling said rectier device, thereby to control the fiow of current through said device to said indicating circuit.

l5. In a signal-receiving apparatus, the combination of Ya signal responsive volume control means having an output circuit, a grid controlled rectiiier device having its control grid connected v'ith said output circuit, an alternating current supply circuit for said device, an indicating device in said circuit, a signal circuit, an electric discharge device in said circuit, said device having a Ygrid connected-with said indicating device, and said last named device being adapted t0 produce a potentialr drop suiicient tobias said discharge device whereby it becomes inoperative to transmit signals through said signal circuit.

16. In a radio receiver, a noise-'suppressor tube having input and output circuits, a controlled tube connected to the output circuit of said noise-k suppressor tube, said controlled tube being adapted to amplify the signals being reproducedby said receiver, means for impressing upon the input of said noise-suppressortube a voltage representative of the average direct-current signal said receiver, a noise-suppressor tube beingA adapted to control the amplication ofV said controlled tube and having input and output cir-l cuits, means ior impressing upon the input of said noise-suppressor tube a voltage representative'of the direct-current component of the received signal, whereby, in the absence of a signal, Y

the noise-suppressor tube will prevent ampliiication by said controlled tube of stray impulses and noises, and means forY regulating the action o said noise-suppressor 'tube'.r

18. In a 4radio receiver, a rcontrolled. 'tube adapted to amplify the signals reproduced by said receiver, a noise-suppressor tube being adapted. to control the amplification of said controlled tube and having input and output circuits, means for impressing upon the input of said noise-suppressor tube a voltage representative of the direct-current component of the received signal, whereby, in the absence of a signal, the noise-suppressor tube will prevent ampliiication by said controlled tube of stray impulses and noises, and means for regulating the action of said noise-suppressor tube, and thereby regulatethelevel of cut-off of said suppressor tube to permit signals of any desired intensity to be reproduced.

19t-In a radio receiver, automatic` means for controlling the amplification of the received radio signals, a'controlled tube adapted to amplify the signals further, a noise-suppressor tube having input and output circuits, said noise-suppressor tube-being adapted to `control automatically thek arnpliiicationY of said controlled tube, means for impressing upon the input of said noise-suppressor tube a voltage representative of the directcurrent component of the amplified signal, whereby, although the amplication is maximum inthe absence of a signal, the noise-suppressor tube will prevent amplification by said controlled tube of stray impulses and noises, and means forVV rived 'from said signal voltage between said cathode and control electrode, a second lvacuum tube having Vat least ananode and a cathode,

said point being negative with respect to the" cathode of said first tube in the absence of a signal, and becoming less negative when the signalstrength increases, whereby the effective impedanceof vsaid first tube is decreased'as said signal voltage increases, and variable means for determining the carrier-frequency signal strength which is'required to substantially decrease the internal'irnpedanceV of said iirst tube.

21. In a radio receiver which includes a `plurality of amplifying tubes, the combination of means for Ydeveloping a direct-current potential,

means for'varying said potential inversely in acy cordance with variations in a radio-frequency current-received by said receiver, circuit connections for applying said'potential-in-'a negative sense to'one of the amplifying tubes of said receiver; the polarity of said potential being such that when said radio-frequency current increases from a low value, said Vpotential becomes more positive, and means for altering upon said ampliner-the elect of the variations in'radio-fr'equency current astransmitted by said direct-current potential.v

22; In a radio receiver tunable over a range of carrier-frequency channels, a system for suppressingY inter-channel disturbances andv signals having voltages below a predetermined level, comprising an amplifying tube, means for applying abiasing voltage-to a control electrode of said tube of a negative valuesuiiicientto prevent said tube from transmitting signals, supplemental means for deriving from the received signal a -uni-directional voltage which varies as the strength of said signal, means for applying said uni-directional voltage to said control electrode in the polarity which renders the bias on said control electrode less negative, and adjustable means for regulating said predetermined voltage level below which disturbances and signals are suppressed.

23. In a radio receiver tunable over a frequency range, means for suppressing interchannel disturbances and voltages below a cut-off level, said means comprising a iirst tube having input and output circuits and a iirst resistor included in said output circuit, a second tube having a control electrode connected to a point of said first resistor, said control electrode having impressed thereon a bias voltage which is more negative than that which-permits said second tube to transmit signals, a rectiiier for deriving from received signals a uni-directional voltage which varies as the strength of said received signals, a second resistor connected in circuit with said rectier across which said unidirectional voltage is developed, and a connection from said second resistor to the input circuit of said first tube, whereby iiuctuations of the uni-directional voltage across said second resistor in response to said received signals produce inverse iiuctuations of the voltage across said first resistor and thereby render the bias on said second tube less negative and thus enable said second tube to be operative when said received signals rise above the cut-off level, and adjustable means for selecting said cut-off level.

24. In a radio receiver, a rectiiier, a controlled tube adapted to amplify the signals being reproduced by said receiver, a Anoise-suppressor tube beingl adapted to control the amplification of said vcontrolled tube and having input and output circuits, and means for impressing upon the input of said noise-suppressor tube a voltage representative of the direct-current component of the rectified signal, and a connection fromthe output circuit of said noise suppressor tube to an initially negatively biased control element of said controlled tube for regulating the bias of said control element, the polarity of said connection being that which causes said bias to become less negative to reduce the internal impedance of said controlled tube when the signal voltage rises above a low value which is below that desired for normal reception, whereby, in the absence of a signal, the noise-suppressor tube will prevent amplication by said controlled tube of stray impulses and noises.

25. An electric circuit arrangement including in effect two electron discharge valves, input terminals for said arrangement, circuit connections for supplying a carrier frequency voltage to said input terminals depending upon the strength of an impressed signal, means for developing a unidirectional output component at a iirst of said valves which varies upon variation of the strength of said voltage, and a connection which impresses at least a portion of said uni-directional component upon a control element of said second valve in the polarity which causes said control element to become more positive when the signal strength increases, whereby the internal impedance of said second valve is decreased as the strength of said impressed signal is increased, and means for impressing an alternating current voltage upon the input ofsaid second valve.

26. In a radio receiver, a carrier-frequency amplifier for amplifying receivedy signals, a second amplifier operating at' a' lower frequency than said carrier-frequency amplifier for further amplifying said signals, a rectifier responsive to the carrier frequency signals for producing a rectified voltage, an automatic volume control system operable by said rectified voltage for controlling the bias of a control electrode of said carrier-frequency amplier, a resistor across which there is developed in response to said rectifier a unidirectional voltage which varies as the strength of said carrier frequency signals when the signals are of lower intensity than that required for normal operation of said receiver, and a noise-suppressing connection from a point of said resistor to a control electrode of said second amplifier, said latter electrode being at such a potential that said noise-suppressing connection biases said control electrode of said second amplifier more positively when the received signal intensity rises above a predetermined value, whereupon the effective impedance of said second amplifier decreases and signals are readily transmitted therethrough.

27. In a carrier frequency signaling system including two electron discharge valves, a circuit arrangement through which alternating current voltages are supplied to the input of each of said valves, means including an impedance for developing at the output of a lirst of said valves a uni-directional voltage responsive to said carrier frequency, which uni-directional voltage varies upon variation of the strength of said impressed signal, a connection from a point of said impedance to a control element of said second valve, said control element having impressed thereon a biasing voltage which is greatly negative when said alternating voltage intensity is relatively small, the polarity of said point being that which causes said element to become less negative when the alternating current voltage increases, whereby the internal impedance ofsaid second valve is decreased as said alternating current voltage increases, and means for adjustably determining the alternating current voltage intensity above which said internal impedance is .substantially decreased.

28. In a carrier signaling system, a vacuum tube, a rectifier having its input circuit connected to a point in said system ahead of said tube, means for producing a direct-current potential in the output of said rectifier which varies as the strength of the carrier Wave supplied thereto, means for applying a biasing voltage derived from said direct-current potential to a control element of said tube, whereby the impedance of said tube Vis effectively decreased when the strength of the ential for illuminating said tuning indicator device in one manner when said network is tuned and in a different manner when it is detuned.

30. In a radioreceiver of the type including a signal tuning device, said device being provided with an illuminable tuning indication dial, an automatic volume control arrangement for determining the response level of said receiver when tuned to a desired signal carrier by said tuning device, a current responsive light producing device disposed in a position adjacent to the dial to illuminate at least a portion thereof, and

means, responsive to the operation of the volume `Y control arrangement, for controlling theY current oW through said light producing device where? Yby a resonance condition of Ythe receiver is determined.

31. In a radio receiver of the type including a signal tuning device, said device being provided with an. illuminable tuning indication dial, an automatic volume control arrangement for determining the response level of said receiver when tuned to a desired signal carrier by said tuning device, a current responsive light producing device disposed in a position adjacent to the dial to illuminate at least a portion thereof, and means,

responsive to the operation of the volume conp trol arrangement, for controlling the current flow through said light producing device whereby a.

resonance condition of the receiver is determined,v and additional means for illuminating said dial disposed adjacent the latter.

32. In a radio receiver of the type including a signal tuning device, said device being provided with an illuminable tuning indication dial, an automatic volume control arrangement for determining the response level of said receiver when tuned to a desired signal carrier by said tuning device, a current responsive light producing de-V vice disposed in a position adjacent to the dial to illuminate at least a portion thereof, and means, responsive to the operation of the volume control arrangement, for controlling the current ow through said light producing device whereby a resonance condition of the receiver is determined, and an apertured screen disposed between said light producing device and the dial to define an area of illumination on the dial.

GEORGE LISLE BEERS. 

